The present invention relates to programmable controllers having a plurality of input and output modules for performing different functions which operate a machine in response to the execution of a control program. More particularly, it relates to an improved module having various features for improving its usage with a programmable controller.
The modules of the type concerned herein are utilized in conjunction with programmable controllers which are connected to industrial equipment such as assembly lines and machine tools, to sequentially operate equipment in accordance with a stored control program. One type of such programmable controller is disclosed in U.S. Pat. No. 4,293,924 and consists of a rack which contains several functional modules. A rack backplane provides signal buses and connectors for electrically coupling the functional modules. One of these modules contains a processor which sequentially executes the control program. The control program is stored in a memory within the processor module and is executed to examine the condition of selected sensing devices on the controlled equipment, or to energize and deenergize selected operating devices on the controlled equipment contingent upon the status of one or more of the examined sensing devices. Also contained within the rack are a number of input/output (I/O) modules, which interface the processor to the sensing and operating devices. These modules can be of various different types, such as a.c. inputs or outputs, d.c. inputs or outputs, analog inputs or outputs, and open or closed loop positioning modules.
The I/O module types can be varied so as to operate a wide variety of equipment. This presents a problem in knowing what particular circuitry is wired to the module so that it can be readily distinguishable from the outside of the module. Further, it is advantageous in utilizing the foregoing modules if the connection for the wiring is readily accessible and an identifiable label could be placed in a panel to identify the circuitry. Other features which can be advantageous are a casing member which includes snap fitment means for engagement with the electrical rack and a rack which includes ventilating openings as well as guide slots for a module circuit board. It would also be helpful in the fabrication of the module if there were provided a self-taping boss on the circuit board terminal block for engagement with the screw to fasten the circuit board to the casing as well as a provision for tying the various wires in a secure manner which are connected to the circuit board terminal block.